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Heat and Thermal Environment
Published in Masanori Shukuya, Bio-Climatology for Built Environment, 2019
The surfaces with so-called selective surface or selective absorber is appropriate for the purpose of solar thermal energy collection because of having high solar absorption while at the same time having low emittance for minimizing the long wavelength radiation dissipating into the surrounding space. Matte white paint is also selective in the opposite implication, that is, very effective in reducing the absorption of solar radiation, while on the other hand, very effective in dissipating the long wavelength radiation into the cold medium such as the clear sky vault, the temperature of which is much lower than the ground surface temperature. This is probably one of the reasons why vernacular buildings in Mediterranean islands are painted matte white as was shown in Fig. 2.4 in Chapter 2.
Enhancement of absorptance of absorber surfaces of a flat plate solar collector using black coating with graphene
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Ramalingam Senthil, K. Kishore Kumar, Kodak Rohan Rajendra, Aniyush Juneja
Based on the results of the conducted experiments, the behavior of graphene as a selective coating with black paint on the mild steel absorber plate is found to be effective. The selective surface coating of the absorber surface plays a vital role in ensuring that maximum solar radiation absorbed. Black paint to graphene ratio of 1:3 by weight-basis shows the highest stagnation temperature of 95.88°C during the indoor testing in 30 minutes with uniform radiation of 800 W/m2 due to the higher absorptance. The value of absorptivity is consistently more than 0.9 up to the wavelength range from 200 to 1500 nm. The average absorptivity of graphene and black paint coating is about 6% more than that of the standard black paint.The surface temperature of graphene and black paint coated surface is observed to be 14.53% more than that of the absorber surface with black paint alone.Further, the graphene-coated FPSC is noted to have about 6.25% more average thermal efficiency than that of black paint at average solar radiation of about 800 W/m2 at the HTF flow rate of 0.2 kg/h.The peak thermal efficiency of FPSC is 46.74% at HTF flow rate of 0.6 kg/h. There is about 8.09% improvement in the collector’s energy efficiency by using paint and graphene (1:3) when compared to that of only black paint.The peak exergy efficiency of FPSC is 4.4% at HTF flow rate of 0.6 kg/h. This is about 12.82% improvement in the collector’s exergy efficiency with graphene.The energy and exergy efficiency of absorber increases with an increase in HTF flow rate.The serpentine flow path air cooling counter-current is also suitable for electronic cooling applications due to the longer duct length. The provision of a serpentine path in the absorber plate is useful in eliminating additional absorber tubes or fins.